1. Field of the Invention
The present invention relates to an automatic transmission to be mounted on an automobile especially to an automatic transmission having a forward four speed automatic transmission mechanism, in detail, relates to a sealing structure at a connecting part to a hydraulic actuator for a certain clutch operation.
2. Description of the Prior Art
Conventionally, the applicant of the present invention has proposed an automatic transmission wherein plural clutches connecting to plural rotation elements and hydraulic clutches to control the plural clutches are whole arranged at a back part of an automatic transmission mechanism. And in a clutch section in which these clutches are housed, a third clutch and a hydraulic actuator to control the third clutch are arranged. By this idea which requires slight modification from the previous structure it is possible to change a three speed automatic transmission mechanism into a four speed automatic transmission mechanism without causing any increase of the cost. (Refer to the Japanese Laid Open Patent No. Sho-62-141344)
A clutch section 47 has, as shown in FIG. 6, a first clutch Cl and a second clutch C2 and is arranged in a transaxle rear cover 17 at the back part of the automatic transmission mechanism. At the back edge of an input shaft 5, a sleeve 5a to enclose a center boss 17a of the cover 17 is arranged. A clutch drum 12 (a flange part) is integrally connected to the sleeve 5a . The clutch drum 12 has a movable member 7 which is spline coupled so that it can move axially. And the movable member 7 encloses a piston member 15 so that it can move axially. The movable member 7 and a cylinder made up by an inside surface of the clutch drum 12 make an oil chamber, and a hydraulic actuator 3 for the first clutch C1 is formed. The piston member 15 and a cylinder made up by the inside surface of the movable member 7 make an oil chamber, and a hydraulic actuator 4 for the second clutch C2 is formed. A spring 10 is arranged between the piston member 15 and a spring receiving member 16 fixed on the sleeve 5a by a snap ring. The spring 10 is a return spring which is used for both piston members 7 and 15 of the hydraulic actuators 3 and 4. Furthermore, the first clutch Cl is placed between a spline arranged on the inner surface of the peripheral section of the clutch drum 12 and a spline arranged on the axially elongated surface of the ring gear R1. The second clutch C2 is placed between a spline arranged on the inner surface of the peripheral section of the movable member 7 and a spline arranged on the outer surface of a hub 50a fixed on the hollow shaft 50.
Oil holes 5b and 5c are arranged in the sleeve 5a to be connected to the oil chambers of the hydraulic actuators 3 and 4. Oil passages 17b and 17c are arranged at the center boss 17a corresponding to the oil holes 5b and 5c. Oil grooves 9a and 9d are arranged so as to surround the oil passages 17b and 17c from both sides. Between the oil passages 17b and 17c an oil groove 9b is arranged. Seal rings 6a, 6b and 6d are installed in the oil grooves 9a, 9b and 9d respectively, which keep the space between the center boss 17a and the sleeve 5a oil-tight, so as not to cause oil leakage from the oil passages 17b and 17c when the hydraulic pressure is supplied to the hydraulic actuators 3 and 4.
In this automatic transmission the first clutch C1 and the second clutch C2 are arranged contiguously and the hydraulic actuators 3 and 4 operating the clutches C1 and C2 are also arranged contiguously. It occurs under certain circumstances that the operation of both clutches C1 and C2 works oppositely to each other, wherein the clutch C1 is kept engaged from the first speed mode to the third, and released at reverse running, but the clutch C2 is engaged at the reverse condition.
By this structure, for example, when the hydraulic pressure is supplied from the oil passage 17b to operate the hydraulic actuator 3, the seal ring 6b moves in the oil groove 9b by the pressure, as shown in FIG. 7 (a), and contacts the right wall of the groove 9b to prevent oil leakage from the groove 9b. When draining the hydraulic actuator 3 to release the first clutch C1 and supplying the hydraulic pressure to the hydraulic actuator 4 to engage the second clutch C2, a space is formed between the center boss 17a and the seal ring 6b because the hydraulic pressure drained from the hydraulic actuator 3 and the hydraulic pressure to be supplied to the hydraulic actuator 4 press the seal ring 6b from the both sides, as shown in FIG. 7(b). By this process a trouble that the oil-tightness is not kept between the hydraulic actuator 3 and the hydraulic actuator 4 occurs.